Viscoelastic melt rheology and time–temperature superposition of polycarbonate–multi-walled carbon nanotube nanocomposites

Abstract

This work investigates the linear and non-linear viscoelastic melt rheology of four grades of polycarbonate melt compounded with 3 wt% Nanocyl NC7000 multiwalled carbon nanotubes and of the matching matrix polymers. Amplitude sweeps reveal an earlier onset of nonlinearity and a strain overshoot in the nanocomposites. Mastercurves are constructed from isothermal frequency sweeps using vertical and horizontal shifting. Although all nanocomposites exhibit a second plateau at ∼10 5 Pa, the relaxation times estimated from the peak in loss tangent are not statistically different from those of pure melts estimated from cross-over frequencies: all relaxation timescales scale with molar mass in the same way, evidence that the relaxation of the polymer network is the dominant mechanism in both filled and unfilled materials. Non-linear rheology is also measured in large amplitude oscillatory shear. A comparison of the responses from frequency and amplitude sweep experiments reveals the importance of strain and temperature history on the response of such nanocomposites.

Influence of processing history on the mechanical properties and electrical resistivity of polycarbonate – multi-walled carbon nanotubes nanocomposites

“…The slower cooling process in CM specimens provides an explanation, promoting a more percolated network and secondary agglomeration, and leading to a wider variation in the CNT network compared to IM specimens. This is consistent with the view that polymer mobility dominates the relaxation processes [3]. A smaller effect contributing to the higher resistivity of IM bars may be orientation of CNTs due to skin effects [9].…”

“…They confirmed that the CNT network consists of weakly bonded clusters that break up and re-agglomerate to form a conductive pathway during the application of shear, suggesting that the destruction of CNT-CNT bonds is reversible. Recent work carried out in our laboratory also confirmed the polymer's role as the dominant relaxation mechanism in these nanocomposite materials [3].…”

Rheological techniques for determining degradation of polylactic acid in bioresorbable medical polymer systems

“…[1], and of PC from ref. [5]. Linear rheology of PLA was measured using a Bohlin C-VOR Instruments rheometer fitted with an environmental chamber.…”

“…One factor that affects the breadth of the distribution is the exponent of 3.4 in Equation (3). There are some suggestions that this exponent can be polymer specific -for instance, values of 4.2 [7] and 5.7 [5] have been reported for PC. A higher exponent narrows the width of the distribution, and therefore it is unlikely that this is the explanation for the discrepancy observed here.…”

“…In a previous study carried out in our laboratory on PC nanocomposites, these parameters were found to be relatively independent of matrix polymer MWD [5]. Research is on-going on the application of this technique to both PC-CNT nanocomposites and degrading PLA-hydroxyapatite nanocomposites.…”